The structures of five pyoverdins occurring in iron-deficient cultures of Pseudomonas fruorescens ATCC 135'25 were elucidated using FAB-MS and 20 NUR techniques; they contain a common partly cyclic pepdde comaining a thirteen-membered ring bound to differently substituted chromophores derived from 2,3-diamino-6,7 dihydroxyquinoline. We define the structure of five of the pyoverdins of Pseuiomonasfluorescens ATCC 13525 as 1. When Pseudomonas fluorescens ATCC 13525 grows in iron deficient conditions, it excretes a large number of pyoverdins possessing the same type of fluorescent chromophore derived from 2,3-diamino-6,7 dihydroxyquinoline, together with deferriferribactin which does not have a chromophore but which also chelates iron(III). Philson and Lliiias 1 have reported an extensive study on one of the major siderophores excreted by the bacteria. They characterized by amino acid analysis and by NMR spectroscopy the nature of the amino acids composing its peptide chain, and have analyzed the nature of its chromophore using UV-visible and NMR spectroscopy. They concluded that the compound was a pyoverdin type of siderophore but did not report any structurel. In an early study on defeniferribactin, an orange-red compound when complexing iron(III) and colorless as a free ligand, Maurer et al. 2 proposed a peptide structure of ten amino acids [Ser(Z), Lys(3), NS -OHOmQ), Tyr( l), Gly(l), Glu( l)] and two acetyl groups. Philson and Lliiias 1 corrected these data showing that deferrlferribactin has only two lysines, and that the two acetyl groups were in fact formyl groups. Although the structures of these molecules have not been fully defined, these preliminary structural studiesstimulated research into iron transport 3 , production of antibodies 4 and improvement of the pyoverdin yield in the culture of Pseudomonasfluorescens ATCC 13525 as a function of the nitrogen source of the medium5.